The present invention relates to an insulated glazing unit having improved thermal insulation properties.
Insulated glazing units are known comprising at least two spaced apart sheets of glass. One such type of insulated glazing unit comprises two sheets of glass spaced apart by perimeter seals and are conventionally known as double glazed units.
Another type of insulated glazing unit comprises two sheets of glass spaced apart by an evacuated space. Disposed in the evacuated space is a plurality of spacers to maintain a spacing of around 1.2 mm between the two sheets of glass. The periphery of the two glass sheets may be sealed with a solder glass, for example as described in EP0860406B1 or an organic material as described in EP1630344A1. This type of insulated glazing unit is often referred to as a vacuum insulated glazing unit, or VIG. VIG's are also described in WO95/15296A1 and EP0999330A1.
It is also known that a VIG may be one pane of a double glazed unit, for example as described in EP0860406B1, EP1030023A1 and U.S. Pat. No. 8,377,524B2. The VIG is spaced apart from another pane, such as a glass sheet. This type of insulated glazing unit has an evacuated low pressure space and an air space (typically filled with an inert gas such as argon or krypton).
It is known that the external surfaces of insulated glazing units such as double glazing units may become fogged due to condensation forming on the outer surfaces. This is a consequence of the emission of heat from the outer glazing. For the surface of a double glazing unit facing the outside i.e. the outer surface, if insufficient heat flows from the internal space to the outer surface, as is the case with insulated glazing units with low U values, the temperature of the outside surface drops. When there is a sufficiently high relative external atmospheric humidity this leads to fogging i.e. condensation or frost deposition, as a result of the temperature of the outer surface falling below the dew point.